A storage system can be provided with a plurality of logical volumes (hereafter referred to as a volume) as a plurality of logical storage devices based on a plurality of nonvolatile physical storage devices (such as an HDD (Hard Disk Drive)). There is a volume that is used as a buffer volume in the plurality of volumes. The buffer volume is a volume that is used as a temporary storage region like a buffer in which data is stored on a temporary basis (see Patent Literature 1 for instance).
A storage system is provided with a cache memory (for instance, a volatile memory) in addition to a physical storage device in general. The storage system receives a write request that specifies a volume from a host computer for instance, stores data (write data) of a write target that conforms to the write request, and returns a response to the host. Hereafter a volume that can be specified by an I/O request (a write request or a read request) from a host computer is referred to as a normal volume in order to distinguish the volume from a buffer volume. The storage system stores write data into a physical storage device that is a basis of a normal volume from a cache memory after responding to the host. A response can be returned to a host after the write data is stored into a normal volume (a physical storage device that is a basis of a normal volume) from a cache memory.
A storage system can also store data that is written to a buffer volume into a cache memory and then store the data from a cache memory to a buffer volume (a physical storage device that is a basis of a buffer volume) at an arbitrary timing in the case in which data is stored into not only a normal volume but also a buffer volume.
There is a journal volume as a buffer volume for instance. A remote copy is to copy a duplicate of a copy source volume (a primary volume) of a primary storage system to a copy destination volume (a secondary volume) of a secondary storage system. For the remote copy, the data of a copy source volume is stored into a journal volume as a journal. A journal volume is used in such a manner that a journal that is corresponded to a write to a primary volume is stored into a leading region at first and other regions in order of precedence for instance. After a journal is stored into a trailing region of a journal volume, the journal volume is used in such a manner a journal is stored into a leading region at first and other regions again.